This invention relates to sensing systems for road vehicles and more particularly it relates to an improved system especially adapted for a dual-stage airbag system with a biased severity measure.
It is already known in the prior art to provide occupant protection systems in road vehicles using airbags having two or more stages of inflation so that the level of inflation is deployed in accordance with the severity of the crash event.
In U.S. Pat. No. 5,999,871 granted to Liu Dec. 7, 1999, a system and method is disclosed for firing airbag inflators simultaneously or in succession to optimize the effect of the airbag for different types of crash at different impact speeds. In this method, the first one of the inflators is triggered by a control algorithm which evaluates the severity of the crash to determine whether to deploy the airbag and when to fire the inflator. In making this determination, the controller detects when vehicle acceleration reaches a threshold, then invokes the deployment algorithm which calculates a deployment time and a velocity change at the deployment time determined by integrating the acceleration. The algorithm for the second stage then evaluates severity of the crash on the basis of the deployment time and velocity at the deployment time. In the case of a very severe crash, the second inflator is fired immediately. For a moderately severe crash, the second inflator is fired after a time delay which is a function of the first stage deployment time and/or the velocity at the first stage deployment time. For a less severe crash, the second inflator is not fired at all. If the system has an additional inflator, the same logic is used to determine its firing based on the deployment time of the second inflator and the velocity at that time. Thus, the system re-determines crash severity as of the time of the inflating of the second stage and deploys the additional inflator when justified by the re-determined crash severity.
U.S. Pat. No. 5,969,599 to Wessels et al. granted Oct. 19, 1999 discloses a method of airbag deployment for occupant protection in a crash event. In this method, deployment is initiated when a filtered version of an acceleration signal exceeds a deployment threshold that is periodically adjusted based on one or more secondary measures of crash severity and the level of event progression. The event progression level is based on the value of a filtered acceleration signal relative to one or more predefined event progression thresholds. The deployment threshold is set to a relatively high default level during periods of inactivity to provide good immunity to rough road impacts while providing timely deployment for high speed crash events; it is periodically adjusted from the default level in the course of a crash event. The level of event progression is determined by deriving a delta-velocity signal biased toward zero, and comparing such signal to a set of predefined event progression thresholds. At each level or stage of the event progression, the deployment threshold is adjusted within predefined boundaries based on one or more secondary measures of crash severity. Threshold adjustments based on each of the secondary measurements are weighted and accumulated to determine the net threshold adjustments.
Watanabe et al. Pat. No. 5,787,377 granted Jul. 28, 1998 describes an airbag ignition timing system which processes vehicle acceleration signals to predict when a passenger""s head will reach a front surface of the airbag. The ignition timing circuit processes acceleration signals to obtain plural displacement signals and adds them together to derive a predicted displacement signal and compare it with a reference value. An ignition signal is issued in the event the predicted displacement signal exceeds the reference value. In this system, predicted occupant displacement and crash severity are processed in a parallel manner as distinguished from a sequential manner.
In accordance with this invention, a crash sensing algorithm is disclosed for a dual stage airbag system which is especially adapted for setting the degree of robustness or sensitivity of the crash sensing system. This is accomplished by using a crash severity measure, referred to herein as a biased severity measure, to determine no deployment, single-deployment or two-stage deployment of an airbag. Preferably, the biased severity measure uses a bias factor to make a chosen severity measure in favor of robustness or sensitivity, as desired.
Further, in accordance with this invention, the crash sensing algorithm uses a predicted occupant movement which must reach a preset occupant movement threshold before the value of the biased severity measure is compared with first and second severity thresholds for determining actuation of the first and second stage deployment of the airbags.
A complete understanding of this invention may be obtained from the detailed description that follows taken with the accompanying drawings.